1. Field of the Invention
This invention generally relates to the separation of gas from a liquid/gas mixture. Here, the present application is directed towards separating gas from an oil/gas mixture with a device that is mounted down a subterranean oil formation.
2. Background Information
It is known that certain oil/gas wells, producing from low pressure formations, require artificial lift such as downhole pumping in order in bring the oil/gas to the surface for recovery. It is also necessary to use downhole pumping equipment in some oil/gas wells which have low pressure due to the formation pressure being expended. The artificial lift devices that are most commonly used include: sucker rod pumps; hydraulic pumps; and electric submersible pumps. The former two devices are both downhole reciprocating pumps which are actuated by a surface pumping unit with sucker rods and a surface hydraulic power fluid unit, respectively. The electric submersible pump, on the other hand, is a centrifugal device powered by an electric motor. It is mounted down-hole in a well.
Most oil wells do produce some gas. However, the presence of the gas, which tends to come out of the oil/gas mixture as it leaves the formation and enters the borehole, can cause operating problems to these pumping devices. Here, gas can become trapped in the pump chamber which causes a loss of efficiency, malfunction of the pump, and even physical damage to the different parts of the pump. This "gas lock" is such a common phenomenon in reciprocating pumps that many wells cannot be produced because the well fluids contain too much gas.
Efforts have been made to separate out the gas from an oil/gas mixture that comes out of the production zone and enters into the pumping devices. For example, U.S. Pat. No. 4,074,763 discloses a tool to be mounted near the end of the production string that uses a series of concentric conduits that generate centrifugal force for separating gas out of the oil/gas mixture. U.S. Pat. No. 4,366,861 separates an oil/gas mixture by reversing the production fluid flow to liberate free gas. Other devices utilize the input of mechanical energy to create centrifugal force to separate oil from gas. These devices are listed as follows: U.S. Pat. Nos.: 3,175,501; 3,972,352; 3,887,342; 3,291,057; 4,386,653; 4,481,020; and re 30,836.
Another conventional method to provide the oil and gas separation is to use a spill-over tube design as illustrated in FIG. 1. While this design allows a good separation of gas and liquid, it has one major drawback. The spill-over tube points upward, which makes retrieval, or fishing operations, of downhole equipment significantly more complicated. To eliminate the disadvantage of the prior art, including the spill-over tube, the present invention was developed.